1. Field of the Invention
The present invention relates to a thermal assisted magnetic recording head, and it particularly relates to a thermal assisted magnetic recording head using a plasmon generator.
2. Description of the Related Art
Recently, in a magnetic recording device typified by a magnetic disk device, in association with high recording density, there is a demand for improvement in performance of thin film magnetic heads and magnetic recording media. As the thin film magnetic head, composite-type thin film magnetic heads are widely used in which a reproducing head having a magneto-resistive effect element (MR element) for reading, and a recording head having an induction-type electromagnetic transducer element for writing, are laminated on a substrate.
The magnetic recording medium is a discontinuous medium where magnetic grains are aggregated, and each magnetic grain has a single magnetic domain structure. Each recording bit on the magnetic recording medium is configured by a plurality of magnetic grains. In order to increase the recording density, asperities at the border between adjacent recording bits need to be decreased by decreasing the size of the magnetic grains. On the other hand, decreasing the size of the magnetic grains, i.e., decreasing in the volume of the magnetic grains, results in a decrease in the thermal stability of magnetization in the magnetic grains. In order to resolve this problem, it is effective to increase the anisotropic energy of the magnetic grains. However, the increased anisotropic energy of the magnetic grains enhances the coercive force of the magnetic recording medium, making it difficult to record the information by an existing magnetic head.
As a method for resolving this problem, so-called thermal assisted magnetic recording is proposed. In this method, a magnetic recording medium with a high coercive force can be used. At the time of recording information, the simultaneous addition of a magnetic field and heat to a portion of the recording medium where the information will be recorded increases the temperature of that portion. This results in information being recorded by the magnetic field at the portion where the coercive force is decreased. Hereafter, the magnetic head used for thermal assisted magnetic recording is referred to as a thermal assisted magnetic recording head (TAMR head).
In thermal assisted magnetic recording, a laser light source is commonly used for heating a magnetic recording medium. As heating methods, a method to heat a magnetic recording medium with laser light (direct heating) and a method to convert the laser light into near-field light (NF light) and heat a magnetic recording medium (NF light heating) are known.
As an example of direct heating, in JP 1110-162444, a head using a solid immersion lens for an optical magnetic disk is disclosed. The head forms a super fine optical beam spot on an optical magnetic disk, and records a signal in a super fine magnetic domain.
As an example of NF light heating, in JP 2001-255254, an NF light probe used for optical recording, i.e., a so-called plasmon antenna is disclosed. The NF light probe is configured with a metallic scatterer in the shape of a conical body or film-like triangle formed on a substrate, and a film, such as a dielectric body formed around the scatterer, and generates NF light from plasmon excited by light. The NF light is a type of so-called electromagnetic field formed around the periphery of a material, and diffraction limitations due to the wavelength of the light can be ignored. By irradiating a microstructure with light having the same wavelength, NF light depending upon the scale of the microstructure is formed, and it is even possible to focus light onto a very small domain on the order of tens of nm.
In JP 2004-158067, an NF light probe used for a single magnetic pole for perpendicular magnetic recording head is disclosed. The NF light probe is a scatterer made of gold, and is formed to be perpendicular to the magnetic recording medium contacting the main pole.
One of the problems of the TAMR head is the reliability of the plasmon antenna against heat. As described in JP 2001-255254 and JP 2004-158067, when light is directly irradiated to the plasmon antenna, the temperature of the plasmon antenna drastically rises, and the thermal reliability decreases. In US2010/0103553, instead of directly irradiating the plasmon antenna with light propagating through the core, a technology is disclosed in which the surface plasmon is excited at a plasmon generator adjacent to the core via a buffer layer. The propagating light is coupled with a plasmon generator in a surface plasmon polariton mode, and excites the surface plasmon at the plasmon generator. Specifically, evanescent light which penetrates the buffer layer is generated at an interface by the total reflection of the light propagating through the core at the interface of the core and the buffer layer. Collective vibration of electric charges in the plasmon generator, i.e., surface plasmon, is coupled with the evanescent light, and the surface plasmon is excited at the plasmon generator. The surface plasmon excited at the plasmon generator propagates to the generator front end surface via a propagation edge, and generates NF light at the generator front end surface. According to this technology, because light that propagates through the core is not directly irradiated to the plasmon generator, it is possible to prevent an excessive temperature increase at the plasmon generator. Such a plasmon generator is referred to as a surface evanescent light coupling type NF light generator.
However, in current TAMR, deterioration of recording characteristics (such as the S/N ratio) in association with continuous recording has been confirmed. As the main factor, agglomeration of the generator front end surface of the plasmon generator is recognized. The agglomeration is a phenomenon where metal atoms gather, and it occurs as a result of diffusion and movement of the metal atoms using heat and stress as the driving force. Asperities exist on an air bearing surface of the magnetic head slider and a surface of the magnetic recording medium, and the generator front end surface of the plasmon generator may make contact with the magnetic recording medium during the operation of the magnetic recording device. The temperature increase and stress increase due to the impact occurring at this time cause the agglomeration. In general, because metal formed by sputtering or a plating method has low density, the density is gradually increased due to heat or stress, and the volume is easily reduced. Since the plasmon generator is normally formed by sputtering, agglomeration and a recess from the air bearing surface in association with the agglomeration easily occur. As a result, the distance between the plasmon generator and the magnetic recording medium is increased, and the capability to heat the magnetic recording medium decreases over time, causing the deterioration of the S/N ratio. Therefore, it is desirable to suppress the agglomeration of the plasmon generator in order to secure the reliability of the TAMR head.
The object of the present invention is to provide a TAMR head with high reliability where the agglomeration of the generator front end surface of the plasmon generator rarely occurs, and the manufacturing method thereof.